This invention relates to the field of the manufacturing of synthesis commercial petrochemical products, and, in particular, to the process of the production of acetone which is commonly used as a solvent and reagent.
The conventional method of the commercial acetone production is a liquid phase cumene oxidation to cumene hydroperoxide with further cleavage of cumene hydroperoxide to phenol and acetone. The oxidation products contain, among the desired products, carbonyl by-products and, in particular, aldehydes. The acetone treatment of aldehydes is difficult. The presence of carbonyl compounds worsens the quality characteristics of the product acetone, namely, greatly decreasing such characteristics as the acetone stability to oxidation with potassium permanganate (the permanganate test).
U.S. Pat. No. 4,885,399 teaches a method to treat ketones from aldehydes through a Tishchenko reaction conducted in the presence of weak Lewis acids. However, a disadvantage of this method is the requirement of a careful preliminary drying of the product or of a synthesis in a special solvent, that complicates the process scheme and makes it more expensive.
Another approach is taught by U.S. Pat. No. 5,399,776. In accordance with the '776 patent, acetone is treated by binding the aldehyde impurities contained in acetone to various diamines followed by distillation of the treated product. However, a disadvantage of this method is that the chemical reagents needed for the treatment are expensive, and the ammonia compounds produced in the reaction have a negative environmental impact.
The most commonly used previously known method to treat acetone from aldehydes is treatment of crude acetone in the presence of an alkaline catalyst based on the reaction of their condensation to form aldoles. Variations of this approach are disclosed in U.S. Pat. Nos. 4,626,600, 4,722,769, and 4,340,447. Each of these patents discloses different process scheme of product acetone rectification in the presence of alkali catalyst.
The '600 patent describes the scheme of the product acetone rectification where the reaction cleavage products containing acetone, phenol, cumene, .alpha.-methylstyrene, water, products of phenol and .alpha.-methylstyrene condensation and impurities are introduced to a rectification column. The main purpose of this column is to separate the reaction cleavage products into acetone and phenol streams. An overhead acetone stream containing acetone, cumene, water and .alpha.-methylstyrene is delivered to a product acetone rectification stage. The rectification of product acetone from the acetone stream is made in two columns. In the first column, only the aldehyde fraction and small acetone recycle flow directed to a CHP cleavage stage are distilled. The entire acetone stream is then delivered to a product acetone column wherein the product acetone is received overhead with a reflux ratio above 5 (the reflux ratio can be reduced to 2.5 in highly efficient columns filled with such packings as Intalox-2T). The bottom products which are a heterogeneous mixture of cumene, .alpha.-methylstyrene and water are delivered to a phase separator. The hydrocarbon fraction from the separator is delivered to further treatment. The water phase is delivered to a neutralization stage of CHP cleavage products. The aqueous alkaline solution is introduced to the neutralization stage with the feed but more often above the feed point (in highly efficient columns filled in with the packings like Intalox-2T it is preferable to feed the aqueous alkali solution only with the feed due to poor alkali solubility in acetone).
The main disadvantage of the scheme of the '600 patent is that the product acetone has low stability to oxidation (a permanganate test shows no more than 4 hours) due to the reversibility of a aldole condensation reaction. Research has shown that aldehydes in the acetone stream containing cumene and water are distributed between organic and water phases at a weight ratio of 2:1. When the acetone stream is treated with the aqueous alkaline solution, aldehydes contained in the water phase do not enter into the aldole condensation reaction. However, aldehydes contained in the organic phase enter easily into the aldole condensation reaction. The majority of the aldole condensation products enter the water phase. Accordingly, the water phase of the acetone stream contains free aldehydes and aldole condensation products. When the acetone stream treated with alkali is rectified at elevated temperatures, the aldole condensation products are partially decomposed. As a result, aldehydes enter the final product. Therefore, the permanganate test of product acetone does not usually exceed 4 hours. At a low efficiency of product acetone rectification column, small amounts of the aldole condensation products enter the final product, decreasing the permanganate test value in addition to the action of the aldehydes.
The '769 patent discloses a scheme of product acetone rectification. This scheme differs from the one taught by the '600 patent as follows: in the '769 patent, the product acetone is rectified with the use of only one rectification column. The reaction cleavage products are delivered to the rectification column, as in the '600 patent, where the acetone stream containing acetone, cumene, water and .alpha.-methylsterene is overhead rectified and then directed to the product acetone column. The acetone stream to the column is introduced as vapor and liquid phases. Aqueous alkali solution is added above the feed point. The product acetone in a liquid phase is removed as a side-draw, the distillate is condensed and its part returns to the column between the feeding and the introduction of the aqueous alkaline solution. The '769 patent insists that for the process to be successful, the optimum regime should remain in the column by controlling the temperature profile because the main aldehyde-alkali interaction proceeds on the trays where simultaneous water and hydrocarbon phases are present. Since the side draw of product acetone is conducted as a liquid phase, the required amount of the liquid on a drawoff tray can be provided for only by large recycle streams due to large reflux stream. A column of large diameter is needed for such a process. Therefore, the energy consumption increases due to the large recycle flows. The '769 patent admits that a disadvantage of the invention disclosed therein is the limitation of the cumene content in the acetone stream. As shown in the patent, the cumene content in the acetone stream cannot exceed 4 wt % in order to produce acetone product of required quality. In many commercial processes the cumene content in the acetone stream is much higher than 4 wt % and commonly reaches 17-20 wt %.
The '447 patent teaches the scheme of product acetone rectification similar to the scheme disclosed in the '769 patent. However, the arrangement disclosed in '447 patent differs from the one taught in the'769 patent in that the acetone stream in the vapor phase containing acetone, water and aldehyde impurities is delivered from the rectification column through a partial condenser to a product acetone column. The phase condensed in the partial condenser is delivered to the rectification column as a reflux. The cumene content in the acetone stream is not provided. The acetone stream is delivered to the product acetone rectification column where the product acetone is rectified as a side-draw. The distillate is condensed and its part is introduced to the reflux flow in the column overhead. The other part of the distillate is introduced to a stage of technical hydroperoxide cleavage. The aqueous alkaline solution in the product acetone column is introduced above the feed point. The alkaline concentration may vary from 0.01 to 5.0 wt. %. The pressure in the product acetone rectification column overhead is kept within the range 0.3-0.8 bars, a temperature in the bottom is kept within the range 80-120.sup..quadrature..quadrature.. The weight ratio of the reflux flow to the side-draw flow ranges from 4:1 to 25:1.
According to the schemes taught by the '769 and '447 patents, acetone of high oxidation stability cannot be produced for the above mentioned reasons. When product acetone is rectified by the schemes described in the '600, '769, and '447 patents, the energy consumption is high due to high reflux ratio.
Therefore it would be desirable to eliminate the said disadvantages and to produce product acetone with higher oxidation stability with the use of the product acetone rectification in the presence of an alkaline catalyst.